Yttria-based refractory composition

ABSTRACT

Method for producing a mold for use in casting reactive metals comprising preparing a slurry of a yttria-based refractory composition and a binder, and using said slurry as a mold facecoat by applying said slurry onto a surface of a mold pattern, wherein said yttria-based refractory composition is obtainable by (a) mixing particles of a yttria-based ceramic material and a fluorine containing dopant, and (b) heating the resulting mixture to effect fluorine-doping of said yttria-based ceramic material.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. application Ser. No.12/443,017, filed on Apr. 23, 2009, which issued as U.S. Pat. No.8,025,094, which is a U.S. National Phase of International ApplicationNo. PCT/AT2008/000173, filed May 15, 2008, which claims the benefit ofEuropean Application No. 07450090.1, filed May 15, 2007. The disclosuresof the foregoing applications are incorporated herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns a yttria-based refractory composition foruse in producing slurries needed for producing ceramic molds for use incasting reactive metals.

2. Description of Prior Art

Aqueous suspensions of ceramic particles, such as yttrium oxide,zirconium oxide, yttria-alumina-zirconia, alumina, and zircon are usedindustrially to form ceramic articles due to their suitability for useas structural materials at high temperatures. These refractory materialsoften are also used for casting super alloys and reactive metals.

An example of such a reactive metal is titanium. Titanium normallyreacts with materials used to form the mould, such as oxides, therebyreleasing oxygen and forming oxygen-enriched titanium. A suspension is asystem in which typically solid particles are uniformly dispersed in aliquid such as water. Particles in the order of less than about 1 μm canbe classified as colloidal particles and a suspension of such particlesis referred to as a colloidal suspension. Such suspensions are used asceramic slurries for different purposes, as mentioned above. Ceramicsnormally are at least partially soluble in water. Furthermore ceramicstend to hydrate, forming a bond with water. To what extent and howquickly ceramics dissolve or hydrate, varies. Moreover, colloidalparticles of ceramics may agglomerate in water. The extent to whichceramics dissolve, hydrate or agglomerate in water based systems dependson many factors, including the nature of the ceramic powder, theoxidation state of the ceramic, the pH; the temperature of the systemand the dispersants which are used.

A lot of methods are known in the art to stabilize colloidal suspensionsi.e. preventing the suspensions from agglomerating, while simultaneouslyreducing the dissolution and hydration rates. For instance, three knownmechanisms include electrostatic, steric and electrosteric mechanisms.These mechanisms are reviewed in detail by Cesarano and Aksay “Stabilityof Aqueous Alpha-Al₂O₃Suspensions with Poly-(methacrylic acid)Polyelectrolyte”, J. Am. Ceram. Soc. 71 p 250-255 (1988).

In the U.S. Pat. No. 5,624,604 to Yasrebi et al. it is told that besidescolloidal dispersion, reducing the attack of water (i.e. hydrationand/or solvation) on the ceramic particle also is an importantconsideration for making commercially suitable ceramic slurries. Ceramicmaterials normally react with water and either partially dissolve(referred to as dissolution or solvation) or form hydrates. The extentof dissolution or hydration varies among different ceramic materials. Asceramic materials dissolve, the dissolved species may substantiallychange the ionic strength of the solution and consequently agglomeratethe particles. In the case of particle hydration, some ceramics form ahydroxide surface layer. However, attack by water also may proceedfarther than the surface layer and may advance into the body of theparticle. As a result, size, morphology and the crystal phase of theparticles may change.

In many commercially important ceramics, such as alumina (Al₂O₃),zirconia (ZrO₂), and zircon (ZrSiO₄) to name a few, the dissolution rateand the extent to which dissolution proceeds is low enough so that itdoes not seem to interfere with their aqueous commercial use; at leastunder mild acidic or basic conditions such as from about pH 3 to aboutpH 11. Furthermore, hydration does not seem to form more than a thinsurface layer, at least when the particle size is equal to or largerthan one micrometer. However, other commercially important ceramics,such as magnesia (MgO), yttria-alumina-zirconia, and Y₂O₃ (yttria),dissolve in an aqueous media to much larger extent and at faster ratesthan the ceramic materials discussed above. As a result, aqueousprocessing of these materials such as magnesia, calcia, yttria,yttria-alumina-zirconia is either difficult or even not practicable.Many attempts have been made by persons skilled in the art of ceramicprocessing to reduce the dissolution and hydration of ceramic particles,while simultaneously keeping the ceramic particles dispersed(unagglomerated) in suspensions. For example, Horton's U.S. Pat. No.4,947,927 teaches that by adjusting the pH of a yttria slurry to high pHvalues in excess of pH 11 one can make yttria intrinsically less solublein water, thereby decreasing its sensitivity to water attack.

Compared to electrostatic stabilization, electrosteric stabilizationprovides a better method for simultaneously dispersing colloidalparticles in suspension and reducing water attack on the ceramicsurface.

The limitations of this method were presented by Nakagawa, M. Yasrebi,J. Liu and I. A. Aksay (“Stability and Aging of Aqueous MgOSuspensions”) at the annual meeting of the Am. Ceram. Soc. (1989). Alsomonomers have been used to prevent the agglomeration of aluminasuspensions. Graule et al. “Stabilization of Alumina Dispersions withCarboxyclic Acids”. Proceedings of the Second European Ceramic SocietyConference (1991).

U.S. Pat. No. 5,624,604 Yasrebi et al. teaches a method for dispersingand reducing the rate of dissolution and/or hydration of colloidalceramic suspensions by adding a non polymeric hydroxylated organiccompound to a ceramic suspension. The ceramic suspension typicallycomprises a colloidal suspension of a metal oxide wherein the metal ofthe metal oxide is an alkali metal, alkaline-earth metal or rare-earthmetal but preferably is magnesium, calcium or a rare-earth metal.

Other methods for increasing the lifetime of a casting slurry aredescribed in U.S. Pat. No. 6,390,179 by Yasrebi et al., thus one featureof the invention is processing refractory powders at a first hydrationlevel to produce powders having a second, lower hydration level beforethe processed materials are used to form casting slurries. Processingaccording to the disclosed methods results in a substantial increase inthe lifetime of a slurry made using such processed materials compared toslurries made using materials not processed as described herein.

U.S. Pat. No. 5,464,797 describes an aqueous ceramic slurry having fromabout 70-weight percent to about 85 weight percent of a fusedyttria-zirconia material. The weight-percent of zirconia in the fusedyttria-zirconia preferably varies from about 1, 0 weight percent toabout 10 weight percent. The slurries of the present invention are usedto form ceramic mold facecoatings for casting reactive materials. Theseslurries are less sensitive to pH-fluctuations than slurries made from100 percent yttria (yttria slurries).

Thus, it is understood that persons skilled in the art of ceramicprocessing have long searched for, and developed methods to increase thelifetime of casting slurries. Despite the prior inventions directed tothis objective, there still is a need for convenient and practicalmethods for increasing the useful lifetimes of investment castingslurries in particular when using other (amongst others AmmoniumZirconium Carbonate, Zirconium Acetate), not colloidal silica based newbinder systems to process such slurries.

In the U.S. Pat. No. 5,827,791 Pauliny et al focused yttria-basedslurries for use in producing ceramic molds for use in the investmentcasting of reactive metals, particularly titanium and titanium, alloys,where the specific preferred binders amongst colloidal silica areammonium zirconium carbonate and zirconium acetate.

Remet Corporation, a leading company in providing binders for thePrecision Investment Casting Industry, offers Ammonium ZirconiumCarbonate (Ticoat®-N) and cites that it is an effective binder systemspecifically for titanium castings. Remet Corporation also offersColloidal Zirconia, that is defined as an acetate stabilized binder forhigh temperature applications.

In the U.S. Pat. No. 4,740,246 Feagin focused relatively unreactive moldcoatings with titanium and titanium alloys that are prepared fromzirconia or yttria sols, or mixtures thereof as a binder for refractorysuch as zirconium oxide, yttrium oxide and mixtures thereof. Feagincites an example, where a cast-sample was made of a slurry containingyttrium oxide and zirconium acetate as essential parts. This sample isvery low in alpha case being less than 0.001 inch.

From U.S. Pat. No. 4,057,433 a mold for casting molten reactive metalsis known, which has a facing portion comprising finely divided particlesof the oxyfluorides of the metals of Group IIIa and a back-up portioncomprising finely divided particles of shell mold back-up material.

The Institution of Electrical Engineers, Stevenage, GB; September 1979(1970-09), Udalova L. V. at AL describe the compaction kinetics of Y2O3doped with 0.4-3.0 wt % LiF at 20-1250° C. and a specific pressure of1000 kg/cm².

Takashima M. published in the Journal of Fluorine Chemistry; ElsevierSequoia, Lausanne, CH, vol. 105, no. 2, September 2000, pages 249-256 anarticle about the “Preparation and properties of binary rare-earth oxidefluorides” which are obtained by the solid-solid reaction betweenrare-earth oxide and fluoride at a temperature higher than 1000° C.

The Institution of Electrical Engineers, Stevenage, GB; November 1980(1980-11), Udalova L. V. et al; describe in the published article“General features of compaction of powders of certain Lithiumfluoridedoped powders” the reaction of pure yttrium oxide powder with lithiumfluoride powder upon compaction at high pressure at room temperature.

SUMMARY OF THE INVENTION

In accordance with the invention and to achieve the objects thereof, thepresent invention is directed to a method for producing a mold for usein casting reactive metals comprising preparing a slurry of ayttria-based refractory composition and a binder, and using said slurryas a mold facecoat by applying said slurry onto a surface of a moldpattern, wherein said yttria-based refractory composition is obtainableby

-   -   (a) mixing particles of a yttria-based ceramic material and a        fluorine containing dopant, and    -   (b) heating the resulting mixture to effect fluorine-doping of        said yttria-based ceramic material.

A preferred embodiment of said method is, wherein said yttria-basedceramic material comprises 50-100 wt.-% Y₂O₃, 0-50 wt.-% Al₂O₃ and 0-50wt.-% ZrO₂.

A more preferred embodiment of said method is, wherein said yttria-basedceramic material is Y₂O₃, a Y/Al/Zr-oxide, a Y/Al-oxide or a Y/Zr-Oxideor combinations thereof.

Another embodiment of said method is, wherein said fluorine containingdopant is one of the group consisting of YF₃, AlF₃, ZrF₄, a lanthanidefluoride and a zirconiumoxyfluoride.

Another more preferred embodiment of said method is, wherein saidyttria-based refractory composition contains 0.10-7.5; preferably1.0-7.5 mass-% fluorine.

In addition to that, the present invention is directed to a method forcasting reactive metals comprising preparing a mold according to themethod described above and casting said reactive metals using said mold.

The present invention is also directed to a Yttria-based refractorycomposition obtainable by

-   -   (a) mechanically mixing particles of a yttria-based ceramic        material and a fluorine containing dopant other than an alkaline        fluoride, and    -   (b) heating the resulting mixture to a temperature within the        range of 300-800° C. to effect fluorine-doping of said        yttria-based ceramic material.

A preferred embodiment of said Yttria-based refractory composition canbe obtained from a yttria-based ceramic material comprising 50-100 wt.-%Y₂O₃, 0-50 wt.-% Al₂O₃ and 0-50 wt.-% ZrO₂.

Said Yttria-based refractory ceramic material preferably is Y₂O₃, aY/Al/Zr-oxide, a Y/Al-oxide or a Y/Zr-Oxide or combinations thereof.

Preferred embodiments for said fluorine containing dopant are YF₃, AlF₃,ZrF₄, a lanthanide fluoride and a zirconiumoxyfluoride.

Another preferred embodiment of said Yttria-based refractory compositioncontains 0.1-7.5, preferably 1.0-7.5 mass-% fluorine.

The present invention is also directed to a method for producing a moldfor use in casting reactive metals comprising preparing a slurry of ayttria-based refractory composition according to present invention and abinder, and using said slurry as a mold facecoat by applying said slurryonto a surface of a mold pattern.

In addition to that, the present invention is directed to a method forcasting reactive metals comprising preparing a mold according to themethod described above and casting said reactive metals using said mold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the results of the slurry-lifetime-test (Method A) withY/Al/Zr-Oxide in Ammonium Zirconium Carbonate and de-ionized water(graph-time versus torque).

FIG. 2 shows the results of the slurry-lifetime-test (Method A) withY/Al/Zr-Oxide in Zirconium-Acetate and de-ionized water (graph-timeversus torque).

FIG. 3 shows the results of the slurry-lifetime-test (Method B) withY/Al/Zr-Oxide in Ammonium Zirconium Carbonate (graph-time versuscinematic viscosity respectively time versus dynamic viscosity).

FIG. 4 shows the results of the slurry-lifetime-test (Method B) withYIAI/Zr-Oxide in Zirconium-Acetate (graph-time versus cinematicviscosity respectively time versus dynamic viscosity).

FIG. 5 shows the results of the slurry-lifetime-test (Method B) withYttria in Ammonium Zirconium Carbonate (graph-time versus cinematicviscosity respectively time versus dynamic viscosity).

FIG. 6 shows the results of the slurry-lifetime-test (Method A) with 0.8wt % F-doped Y/Al/Zr-Oxide in Zirconium-Acetate and de-ionized water(graph-time versus torque).

FIG. 7 shows the results of the slurry-lifetime-tests (Method A) incomparison of Y/Al/Zr-Oxide to 0.8 wt % F-doped Y/Al/Zr-Oxide inAmmonium Zirconium Carbonate and de-ionized water (graph-time versustorque).

FIG. 8 shows the results of the slurry-lifetime-test (Method A) with 1.0wt % F-doped Y/Al/Zr--Oxide in Ammonium Zirconium Carbonate andde-ionized water (graph-time versus torque).

FIG. 9 shows the results of the slurry-lifetime-tests (Method A) incomparison of 1.9 wt % F-doped Yttria (Zirconium oxyfluoride) to 1.7 wt% F-doped Yttria (Lithium fluoride) in Ammonium Zirconium Carbonate(graph-time versus torque).

FIG. 10 shows the results of the slurry-lifetime-test (Method B) with1.0 wt % F-doped Y/Al/Zr-Oxide in Zirconium-Acetate (graph-time versuscinematic viscosity).

FIG. 11 shows the results of the slurry-lifetime-test (Method B) with1.1 wt % F-doped Y/Al/Zr-Oxide in Zirconium-Acetate (graph-time versuscinematic viscosity).

FIG. 12 shows the results of the slurry-lifetime-test (Method B) with2.4 wt % F-doped Y/Al/Zr-Oxide in Ammonium Zirconium Carbonate(graph-time versus cinematic viscosity).

FIG. 13 shows the XRD-analysis of 2.4 wt % F-doped Y/Al/Zr-Oxide. FIG.14 is the TEM picture of 2.4 wt % F-doped Y/Al/Zr-Oxide, where viaelectron energy loss spectroscopy a Fluorine-signal can be detected atthe grain boundary area; 200 nm below the boundary area, there exists noFluorine-peak.

FIG. 15. is the Jump-ratio image (elemental maping of oxygen) of 2.4 wt% F-doped Y/Al/Zr-Oxide, where a 170 nm wide layer of YOF can beobserved along the grain boundary.

FIG. 16 is the diffraction image of the inside of the grain of 2.4 wt %F-doped Y/Al/Zr-Oxide, where Y₂O₃ can be verified.

FIG. 17 is the diffraction image of the boundary grain of 2.4 wt %F-doped Y/Al/Zr-Oxide, where YOF can be verified.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides new yttria-based materials for increasingthe lifetime of casting slurries. One feature of the invention isprocessing such refractory powders which exhibit a significantly reducedrate of dissolution and/or hydration, when used in colloidal ceramicsuspensions. This can be accomplished at any pH according to the presentinvention, thereby making it possible to reduce the aging of rare earthbased slurries considerably.

The present invention also encompasses the use of compositionscomprising an aqueous slurry of yttria-based particles doped with anamount of fluor effective to reduce the dissolution rate of theparticles mentioned above. One skilled in the art will realize that an“effective amount” may vary from composition to composition. However, aneffective amount typically means an amount of at least about 0.1 weightpercent. Yttria-based refractory composition according to the presentinvention contain at least 0.1 wt.-% fluorine.

The dopant material is a fluoride or oxyfluoride or compounds that formsuch dopants as mentioned above upon further processing, wherein thesefluorides or oxyfluorides are of metals especially selected from thegroup consisting of aluminium, zirconium, yttrium and lanthanides.

Doped yttria (Y₂O₃), yttria alumina (Y/Al-oxide), yttria aluminazirconia (Y/Al/Zr-oxide) or yttria zirconia (Y/Zr-oxide) particlesaccording to the present invention are not simply a binary mixture ofthe dopant and yttria or yttria-alumina-zirconia or yttria-zirconia.Instead, the phrase “doped particles” or similar phrases used herein,refers to an intimate mixture of yttria or yttria-alumina-zirconia oryttria-zirconia or yttria-alumina. “Intimately mixed” or “intimatemixture” is used to differentiate binary mixtures that result simplyfrom the physical combination of two components. Typically, an “intimatemixture” means that the dopant material is atomically dispersed inyttria or yttria-alumina-zirconia or yttria-zirconia such as with asolid solution or as small precipitates in the crystal matrix of thesolid yttria or yttria-alumina-zirconia or yttria-zirconia oryttria-alumina.

Alternatively, an intimate mixture may refer to compounds that arefused, such as, yttria or yttria-alumina-zirconia or yttria-zirconia oryttria-alumina. By way of example and without limitation, the dopantsmay be intimately mixed with yttria or yttria-alumina-zirconia oryttria-zirconia or yttria-alumina in the following ways: 1. finelydispersed in the yttria or yttria-alumina-zirconia or yttria-zirconia oryttria-alumina matrix or 2. provided as a coating on the surface of suchparticles or provided as a diffused surface layer of dopant on the outersurface of yttria or yttria-alumina-zirconia or yttria-zirconia oryttria-alumina particles. The dopant may be in solid solution with thematrix, or it may be in the form of small precipitates in the crystalmatrix, or it may be a coating on the surface of the particle orportions thereof.

Without limiting the scope of this invention to one theory of operation,it is currently believed that the dopant shields dissolution sites onthe surface of the yttria or yttria-alumina-zirconia or yttria-zirconiaor yttria-alumina from attack by solvent molecules, such as water. Inother words, the dissolution and/or hydration of these particlesprimarily is a surface reaction, and the dopant interferes with thissurface reaction. Consequently, the dissolution rate of yttria oryttria-alumina-zirconia or yttria-zirconia or yttria-alumina isdecreased due to the formation of yttrium oxyfluorides, on the surfaceof the above mentioned refractory powders.

For this reason and in the absence of any particle breakage, only aminor portion of the outer surface regions of the refractory powdersrelated to this invention actually need to be doped. This means that thecore of the particle may remain substantially pure yttria, yttriaalumina, yttria alumina zirconia or yttria zirconia.

In the following, a general description of the production process of thepreferred F doped yttria-based ceramic materials is given.

The dopant (a fluorine-containing substance, for instance YF₃, zirconiumoxyfluoride, AlF₃) is added to the raw material flour (preferred:yttria, yttria-alumina-zirconia, yttria-zirconia, yttria-alumina). Inorder to distribute the two flours homogenously, they are accuratelyblended respectively ground together and afterwards sieved. Subsequentlythe flour-mixture is heated, e.g. calcined to form a YOF-surface layeron the outer surface of the ceramic particles.

In the present invention F-doped Yttria-based refractories are producedat a preferred temperature range from 300 to 800 degrees. Treating theF-doped materials at a temperature higher than 800 degrees (Takashima M.describes in “Preparation and properties of binary rare-earth oxidefluorides” by Takashima M. temperatures higher than 1000° C.) causes adecrease of slurry stability of the F-doped Yttria based refractory inwater based binder systems.

Contrary to the publication “General features of compaction of powdersof certain Lithium fluoride doped powders”, where the powder and thedopant (Lithium fluoride) are mixed chemically; the fluorine containingdopant and the Yttria-based flour are mixed mechanically in the presentinvention. Furthermore no specific pressure is used for the productionof the preferred Yttria-based refractories as described in thepublication mentioned above and as described in “Compaction kinetics ofLithium fluoride-doped Yttrium oxide” written by Udalova et al.

Lithium fluoride and alkali metals are not used as dopants according tothe present invention, due to their negative effect on the slurrystability in water-based binder systems.

EXAMPLES

To further illustrate the production of F-doped Y₂O₃, Y/Al/Zr-Oxide,Y/Zr-Oxide, Y/Al-Oxide and their effect on increasing the slurrylifetime following examples and the results of their slurrylifetime-tests are provided. The fluorine-contents that are indicated inthe examples accord to the results of the chemical analysis of thematerials used. The analysis was made by realising soda respectivelysoda potash pulping and by using an ion selective electrode.

First the two methods that were used for detecting the slurry lifetime,are described.

1. Measurement of the Torque—Method A

The experimental setup consists of

-   -   double jacket assay container made of stainless steel (inner        diameter=5 cm, external diameter=7 cm), a Plexiglas cap and        sealing member (stainless steel) therefore. In the middle of the        cap there is a hole (bore=0.9 cm) for the mixer (shaft        diameter=0.8 cm). The cap is sealed up with a grommet.    -   agitator (IKA EUROSTAR power control-visc P4) and a horseshoe        mixer (width=4.5 cm, altitude=5.5 cm)    -   measuring instrument for detecting the dynamic torque, which        acts on the agitating element (IKA VISKOKLICK® VK 600 control).        The measuring unit transforms the dynamic into a static torque.    -   thermostat (LAUDA ecoline RE 106)    -   software labworldsoft 4.01

First the slurry is formulated (exact composition of the slurry seedescription of the examples) and then filled into the double jacketassay container, which is temperature controlled at 25° C. by athermostat. The agitator with a horseshoe mixer works with a constantrotation speed of 30 revolutions per minute. The horseshoe mixer ispositioned just 1-2 mm above the bottom of the assay container. At thebeginning of the test the torque is reset and then recorded over time.Therewith the developing of the relative viscosity can be observed. Foranalysis the point of the first significant increase in slope is definedas the slurry-lifetime.

2. Measurement of the Cinematic Viscosity Using Zahn Cup RespectivelyMeasurement of the Dynamic Viscosity Using Rheometer—Method B

The experimental setup consists of

-   -   a roller    -   Polyethylen-bottle (2 L) (Bartelt) with cap    -   Zahncup Nr. 4 (ERICHSEN GMBH & CO KG) respectively Rheometer        Physica MCR 301 (Anton Paar GmbH)—Plate-Plate-System (PP50;        measuring gap=0.5 mm unless otherwise noted; measuring        temperature=25° C., viscosity value at a shear rate of 100/s).

Powder and binder (exact composition of the slurry see description ofthe examples) are mixed in the PE-bottle with an agitator and then puton the roller that has a constant rotation speed. The rotation speed ofthe bottle is 16.5 rpm. The slurry is stirred uniformly at roomtemperature and after one hour of stirring the start-viscosity ismeasured with Zahncup Nr. 4-unless otherwise noted (determining theefflux time and convert it to the cinematic viscosity according to theadequate formula of ASTM D 4212) or/and with the Rheometer. In certaintime intervals (˜every 3-5 hours) and when the viscosity starts toincrease, viscosity-measurements are done every two respectively everyhour. For analysis the doubling of the start viscosity [cSt] is definedas the slurry lifetime. If the doubling of the viscosity takes placebetween two measurements, a straight line is built between these twomeasuring points, and the value of the doubling of the viscosity iscalculated from the linear equation.

Slurry Composition

In the present invention the slurry is formed by mixing an aqueous basedbinder with e.g. yttria, yttria-alumina-zirconia, yttria-alumina oryttria-zirconia. The preferred binders are

-   -   Ammonium Zirconium Carbonate solution which finds use as a        binder for titanium alloy casting (Ticoat®-N)    -   Zirconium Acetate, an acetate stabilized Zirconia sol (binder).        Production of Yttria-Alumina-Zirconia

Appropriate quantities of Y₂O₃, ZrO₂ and Al₂O₃ are mixed, put into anelectric furnace and fused at the melting temperatures of the materials.After this operation the melt is cooled to get an ingot. The ingotobtained is crushed into particles of below 3 mm using a jaw crusher.Afterwards the particles are annealed.

COMPARATIVE EXAMPLES Results of Slurry-Lifetime-Tests with StandardMaterials Measurement of the Torque—Method A Comparative Example 1

250 g of fused Y/Al/Zr (95.88/0.12/4.0) flour (TIAG) were mixed with44.8 g of Ammonium Zirconium Carbonate and 22.11 g de-ionised water. Thestart viscosity of the slurry didn't change for 0.9 hour, but then thetorque and therewith the viscosity increased dramatically. After 1.4hours the torque rose up to 25 Ncm (FIG. 1).

Comparative Example 2

250 g of fused Y/Al/Zr (95.88/0.12/4.0) flour (TIAG) were mixed with44.8 g of Zirconium Acetate and 22.11 g de-ionised water. The startviscosity of the slurry didn't change for 0.7 hours, but then the torqueand therewith the viscosity increased dramatically (FIG. 2).

Measurement of the Viscosity Using Zahncup Respectively UsingRheometer—Method B Comparative Example 3

1200 g of fused Y/Al/Zr-Oxide (95.88/0.12/4.0) flour (TIAG) were mixedwith 360 g of Ammonium Zirconium Carbonate.

Because of the low start viscosity of the slurry, Zahncup measurementswith Zahncup Nr. 3 and 4 were done. Accessorily viscosity measurementswith the Rheometer were realised. You can see the results in FIG. 3.After three hours the start-viscosity increased by 112 percent (Zahncup4). At this point no reproducible measurements could be realised withZahncup Nr. 3 because of the high slurry viscosity. After 4 hours theefflux time of the slurry couldn't be determined likewise with ZahncupNr. 4 anymore (efflux time>2 minutes).

Comparative Example 4

1200 g of fused Y/Al/Zr-Oxide (95.88/0.12/4.0) flour (TIAG) were mixedwith 300 g of Zirconium Acetate. Viscosity measurements were made withZahncup Nr. 4 and Rheometer. You can see the results in FIG. 4. Becauseof the rapid increase of the viscosity, the start viscosity was measuredafter 5 minutes of stirring using the roller. After 35 minutes the startviscosity increased by 128 percent, after 60 minutes the slurry couldnot be measured with Zahncup Nr. 4 anymore, the viscosity increaseddramatically.

Comparative Example 5

1200 g of fused Yttria flour (TIAG) were mixed with 360 g of AmmoniumZirconium Carbonate. Viscosity Measurements were made with Zahncup Nr. 4and Rheometer. After 125 minutes the start viscosity increased by 39.2%,after 185 minutes the slurry could not be measured with Zahncup Nr. 4anymore (efflux time>2 min), the viscosity increased dramatically. (FIG.5)

With the following examples the invention is described in more detail:

Example 1

6.85 kg fused block material of Y/Al/Zr (95.88/0.12/4.0) were milled for90 minutes in a ZrO₂-lined ball mill (ZOZ GmbH TYP COMB 03-A03).Therefore 25 kg 1.25″ grinding-balls (Yttria stabilized Zirconium Oxide)were used. After the addition of 150.5 g (=2.15 wt %) Yttriumfluoridethe powder mixture was milled for another 60 minutes. The milled productwas sieved <45 μm and then calcined (Nabertherm C250) inAl₂O₃(0.9)-mullite(0.1)-crucibles (1.5 kg per crucible). The heatingrate was 5° C./min up to a temperature of 550° C. that was maintainedfor 6 hours 50 min.

Life Time Test (Method A)

250 g of the 0.8 wt % F-doped material were mixed with 44.8 g ofZirconium Acetate and 22.11 g de-ionised water. The slurry lifetime was41 hours. (FIG. 6). From this time on the viscosity increased sharply.After 50 hours a torque of 25 Ncm was achieved.

Example 2

Powder-production was performed according to Example 1.

Life Time Test (Method A)

250 g of 0.8 wt % F-doped material were mixed with 44.8 g of AmmoniumZirconium Carbonate and 22.11 g de-ionised water. The slurry lifetimeaccounted for 56 hours (see FIG. 7: Example 2 in comparison to theuntreated Y/Al/Zr-Oxide).

Example 3

Powder-Production

Fused Y/Al/Zr-Oxide-flour (95.88/0.12/4.0) was milled with 3.3 wt %Zirkonylfluoride with a planetary mill (ZrO₂ grinding jars and balls)for 10 minutes. The weighted sample was 96.7 g Y/Al/Zr-flour and 3.3 gZirkonylfluoride per grinding jar-four jars were used. (production ofZirkonylfluoride by fractionally converting Zirconium Carbonate with HFand following calcination at 450° C. for 4 hours). The powder mixturewas calcined in a ZrO₂-crucible at 550° C. for 3 hours using a mufflekiln (Heraeus Holding GmbH MR 170 E).

Life Time Test (Method A)

250 g of the 1.0 wt % F-doped material were mixed with 44.8 g ofAmmonium Zirconium Carbonate and 22.11 g de-ionised water. The slurrylifetime added up to 124 hours. (see FIG. 8)

Example 4

Powder-Production

Raw materials and milling parameters according to Example 1. The milledproduct was sieved <45 μm and then calcined (High temperature kiln) inAl₂O₃(0.9)-mullite(0.1)-crucibles (1.5 kg per crucible). The heatingrate was 5° C./min up to a temperature of 540° C. that was maintainedfor 8 hours.

Life Time Test (Method A)

250 g of 0.9 wt % F-doped material were mixed with 62.5 g of ZirconiumAcetate. The slurry lifetime was 66 hours.

Example 5

Fused Y/Al/Zr-Oxide-flour (95.88/0.12/4.0) was milled with 2.2 wt %Zirkonium(IV)fluoride (99.9%—Sigma Aldrich) with a planetary mill (ZrO₂grinding jars and balls) for 10 minutes. The weighted sample was 107.6 gY/Al/Zr-flour and 2.4 g Zirkonium(IV)fluoride per grinding jar—four jarswere used. The powder mixture was calcined in a ZrO₂-crucible at 550° C.for 3 hours using a muffle kiln (Heraeus Holding GmbH MR 170 E).

Life Time Test (Method A)

250 g of the 0.8 wt % F-doped material were mixed with 44.8 g ofAmmonium Zirconium Carbonate and 22.11 g de-ionised water. The slurrylifetime was 380 hours.

Example 6

6.490 kg fused block material of Yttria were milled for 30 minutes in aball mill (ZOZ GmbH TYP COMB 03-A03; 20 kg 1.25″ grinding-balls (Yttriastabilized Zirconium Oxide other milling parameters as described inExample 1). After the addition of 0.510 kg (=7.3 wt %)Zirconiumoxyfluoride Zr₇O_(8.79)F_(9.71) the powder mixture was milledfor another 90 minutes. The milled product was sieved <63 μm and 399.5 gwere calcined in a ZrO₂-crucible at 400° C. for 4 hours using a mufflekiln (Heraeus Holding GmbH MR 170 E).

Life Time Test (Method A)

250 g of the 1.9 wt %-F-doped material were mixed with 75 g of AmmoniumZirconium Carbonate. A significant increase of the measured torque couldnot be observed for more than 335 hours. Afterwards the experiment wasstopped.

Example 7

Yttium-Oxide-flour was milled with 2.7 wt % Lithium fluoride(99.995%—Sigma Aldrich) with a planetary mill (ZrO₂ grinding jars andballs) for 10 minutes. The weighted sample was 97.3 g Yttria and 2.7 gLithium fluoride per grinding jar. The powder mixture (398.7 g) wascalcined in a ZrO₂-crucible at 400° C. for 4 hours using a muffle kiln(Heraeus Holding GmbH MR 170 E).

Life Time Test (Method A)

250 g of the 1.7 wt %-F-doped material were mixed with 75 g of AmmoniumZirconium Carbonate. The first significant increase in slope wasobserved at 10 hours. (See FIG. 9—Example 6 in comparison to Example7—Yttria doped with LiF.)

Example 8

6.787 kg fused block material of Y/Al/Zr (95.88/0.12/4.0) were milledfor 30 minutes in a ball mill (ZOZ GmbH TYP COMB 03-A03; millingparameters as described in Example 1). After the addition of 213 g (=3wt %) Yttrium-Fluoride the powder mixture was milled for another 90minutes. The milled product was sieved <75 tun and then calcined(Nabertherm C250; 1.5 kg per Al₂O₃(0.9)-mullite(0.1)-crucible). Theheating rate was 1.1° C./min up to a temperature of 550° C. that wasmaintained for 8 hours.

Life Time Test (Method B)

1200 g of 1.0 wt % F-doped Y/Al/Zr were mixed with 300 g of ZirconiumAcetate. After one hour the initial viscosity was 400 cSt. The slurrylifetime added to 72 hours, at this point the start viscosity hasdoubled (FIG. 10).

Example 9

6.664 kg fused block material of Y/Al/Zr-Oxide (95.88/0.12/4.0) weremilled for 60 minutes in a ball mill (ZOZ GmbH TYP COMB 03-A03; millingparameters as described in Example 1). After the addition of 336 g (=4.8wt %) Zirconiumoxyfluoride Zr₇O_(8.79)F_(9.71) the powder mixture wasmilled for another 90 minutes. The milled product was sieved <63 μm andthen calcined (Nabertherm C250; 1.5 kg perAl₂O₃(0.9)-mullite(0.1)-crucible). The heating rate was 1.1° C./min upto a temperature of 450° C. that was maintained for 4 hours.

Life Time Test (Method B)

1200 g of 1.1 wt % F-doped Y/Al/Zr were mixed with 300 g of ZirconiumAcetate. After 171.5 hours the initial viscosity of 295 cSt rose up to547 cSt. This means that the viscosity increased by 85% after 171.5hours. (FIG. 11)

Example 10

6.348 kg fused block material of Y/Al/Zr (95.88/0.12/4.0) were milledfor 30 minutes in a ball mill (ZOZ GmbH TYP COMB 03-A03; millingparameters as described in Example 1). After the addition of 652 g (=9.3wt %) Zirconiumoxyfluoride Zr₇O_(8.79)F_(9.71) the powder mixture wasmilled for another 120 minutes. The milled product was sieved <63 μm andthen calcined (Nabertherm C250; 1.5 kg perAl₂O₃(0.9)-mullite(0.1)-crucible). The heating rate was 1.1° C./min upto a temperature of 650° C., that was held for 13 hours.

Life Time Test (Method B)

1200 g of 2.2 wt % F-doped Y/Al/Zr were mixed with 360 g of AmmoniumZirconium Carbonate. The initial viscosity of 314 cSt doubled after 28.7hours.

Example 11

Powder production according to Example 10. The heating rate of thecalcination was 1.1° C./min up to a temperature of 450° C., that wasmaintained for 7 hours.

Life Time Test (Method B)

1200 g of 2.4 wt % F-doped Y/Al/Zr were mixed with 360 g of AmmoniumZirconium Carbonate. After 70.3 hours the initial viscosity of 232 cStdoubled (see FIG. 12).

X-Ray-Diffraction (XRD) Analysis

A XRD-analysis of the material described in Example 11 was made. Thedetected phases are Y₂O₃, ZrO₂, YOF and Zr_(0.72)Y_(0.28)O_(1.862) (FIG.13).

Transmission Electron Microscopy (TEM)-Analysis

A TEM analysis of the material described in Example 11 was made at theAustrian Centre for Electron Microscopy and Nanoanalysis in Graz.Therefore a lamella out of a grain, that showed a Fluorine-peak at theprecedent Energy dispersive X-ray spectroscopy (EDX), was removed usingFocused Ion Beam (FIB).

Via electron energy loss spectroscopy a Fluorine-signal could bedetected at the grain boundary area. (see FIG. 14). 200 nm below theboundary area, there exist no Fluorine-peak. At the so called Jump-ratioimage (eliminating the background signal by dividing the signal image bya background image) a 170 nm wide layer along the grain boundary isapparent (FIG. 15—elemental map of oxygen) that is verified asYttrium-Oxy-Fluoride in the following. At the diffraction images of theinside of the grain Y₂O₃ can be detected (FIG. 16) and at thediffraction image of the grain boundary the chemical compoundYttrium-Oxyfluoride (YOF) can definitely be verified (FIG. 17). Via EDXthe element Zirconium can also be detected in the layer at the surfaceof the grain.

Example 12

6.520 kg fused block material of Y/Al/Zr (95.88/0.12/4.0) were milledfor 30 minutes in a ball mill (ZOZ GmbH TYP COMB 03-A03; millingparameters as described in Example 1). After the addition of 480 g (=6.9wt %) Zirconiumoxyfluoride Zr₇O_(8.79)F_(9.71) the powder mixture wasmilled for another 120 minutes. The milled product was sieved <63 μm andthen calcined (Nabertherm C250; 1.5 kg perAl₂O₃(0.9)-mullite(0.1)-crucible). The heating rate was 1.1° C./min upto a temperature of 400° C., that was maintained for 4 hours.

Life Time Test (Method B)

1100 g of 1.7 wt % F-doped Y/Al/Zr were mixed with 304.7 g of AmmoniumZirconium Carbonate. The formulated slurry showed a lifetime of 44.9hours.

Example 13

6.974 kg fused block material of Y/Al/Zr (95.88/0.12/4.0) were milledfor 30 minutes in a ball mill (ZOZ GmbH TYP COMB 03-A03; 20 kg 1.25″grinding-balls (Yttria stabilized Zirconium Oxide—other millingparameters as described in Example 1). After the addition of 0.026 kg(=0.37 wt %) Zirconiumoxyfluoride Zr₇O_(8.79)F_(9.71) the powder mixturewas milled for another 120 minutes. The milled product was sieved <63 μmand then calcined (Nabertherm C250; 1.5 kg perAl₂O₃(0.9)-mullite(0.1)-crucible). The heating rate was 1.1° C./min upto a temperature of 400° C., that was maintained for 4 hours.

Life Time Test (Method B)

1200 g of 0.1 wt % F-doped Y/Al/Zr were mixed with 360 g of AmmoniumZirconium Carbonate. The formulated slurry showed a lifetime of 21.6hours.

Example 14

5.212 kg fused block material of Y/Al/Zr (95.88/0.12/4.0) were milledfor 30 minutes in a ball mill (ZOZ GmbH TYP COMB 03-A03; 20 kg 1.25″grinding-balls (Yttria stabilized Zirconium Oxide—other millingparameters as described in Example 1). After the addition of 1.788 kg(=25.5 wt %) Zirconiumoxyfluoride Zr₇O_(8.79)F_(9.71) the powder mixturewas milled for another 120 minutes. The milled product was sieved <63 μmand then calcined (Nabertherm C250; 1.5 kg perAl₂O₃(0.9)-mullite(0.1)-crucible). The heating rate was 1.1° C./min upto a temperature of 400° C., that was maintained for 4 hours.

Life Time Test (Method B)

1200 g of 6.9 wt % F-doped Y/Al/Zr were mixed with 440 g of AmmoniumZirconium Carbonate. After a certain time the volume of the slurry wastoo small to realise Zahncup Nr. 5 measurements. Therefore Rheometermeasurements (measuring gap=1 mm) were made. First every weekday,afterwards approximately every week one respectively two measurementswere realised. A tendency of slight increase of viscosity could beobserved after 110 days, but no significant increase of the viscosity ofthe formulated slurry could be observed for 152 days. Afterwards theexperiment was stopped.

Example 15

6.490 kg fused block material of Yttria were milled for 30 minutes in aball mill (ZOZ GmbH TYP COMB 03-A03; 20 kg 1.25″ grinding-balls (Yttriastabilized Zirconium Oxide—other milling parameters as described inExample 1). After the addition of 0.510 kg (=7.3 wt %)Zirconiumoxyfluoride Zr₇O_(8.79)F_(9.71) the powder mixture was milledfor another 90 minutes. The milled product was sieved <63 μm and thencalcined (Nabertherm C250; 1.5 kg per Al₂O₃(0.9)-mullite(0.1)-crucible).The heating rate was 1.1° C./min up to a temperature of 400° C., thatwas maintained for 4 hours.

Life Time Test (Method B)

1200 g of 1.9 wt % F-doped Yttriumoxide were mixed with 360 g ofAmmonium Zirconium Carbonate. After 74.1 hours the initial viscositydoubled.

Example 16

The production of the F-doped Yttria was carried out as described inExample 15. The heating rate of the calcination was 1.1° C./min up to atemperature of 1100° C., that was maintained for 4 hours.

Life Time Test (Method B)

1200 g of 1.9 wt % F-doped Yttriumoxide were mixed with 360 g ofAmmonium Zirconium Carbonate. Due to the temperature treatment at 1100°C. relatively strong agglomerates were formed, in order to disperse theparticles homogenously and to break down the agglomerates, powder andbinder were mixed additionally to the agitator with an Ultra Turrax T25(60 sec 17500 l/min and 20 sec 21500 l/min). In this case the initialviscosity is taken from the measurement at 4 hours after the beginningof the experiment. Due to the sample preparation the slurry viscosity at1 hour was lower (temperature of the slurry was increased) than thearisen balanced viscosity after 4 hours (292 cSt). After 26.5 hours theviscosity has doubled.

Example 17

The production of the F-doped Yttria was carried out as described inExample 15. The heating rate of the calcination was 1.1° C./min up to atemperature of 900° C., that was maintained for 4 hours.

Life Time Test (Method B)

1200 g of 2.0 wt % F-doped Yttriumoxide were mixed with 360 g ofAmmonium Zirconium Carbonate. Due to the temperature treatment at 900°C. relatively strong agglomerates were formed, in order to disperse theparticles homogenously and to break down the agglomerates, powder andbinder were mixed additionally to the agitator with an Ultra Turrax T25(30 sec 17500 l/min and 10 sec 21500 l/min).

The slurry showed a lifetime of 26.9 hours.

Example 18

The production of the F-doped Yttria was carried out as described inExample 15. The heating rate of the calcinations was 1.1° C./min up to atemperature of 800° C., that was maintained for 4 hours.

Life Time Test (Method B)

1200 g of 1.9% F-doped Yttriumoxide were mixed with 360 g of AmmoniumZirconium Carbonate. Due to the temperature treatment at 800° C.agglomerates were formed, in order to disperse the particleshomogenously and to break down the agglomerates, powder and binder weremixed additionally to the agitator with an Ultra Turrax T25 (30 sec13500 l/min)

The slurry showed a lifetime of 33.4 hours.

Example 19

The production of the F-doped Yttria was carried out as described inExample 15. The heating rate was 1.1° C./min up to a temperature of 300°C., that was maintained for 4 hours.

Life Time Test (Method B)

1200 g of 2.0% F-doped Yttriumoxide were mixed with 360 g of AmmoniumZirconium Carbonate. The slurry showed a lifetime of 50.3 hours.

Example 20

6.569 kg fused block material of Yttria were milled for 30 minutes in aball mill (ZOZ GmbH TYP COMB 03-A03; 20 kg 1.25″ grinding-balls (Yttriastabilized Zirconium Oxide—other milling parameters as described inExample 1). After the addition of 0.431 kg (=6.2 wt %) Yttrium fluorideYF₃ the powder mixture was milled for another 90 minutes. The milledproduct was sieved <63 μm and then calcined (Nabertherm C250; 1.5 kg perAl₂O₃(0.9)-mullite(0.1)-crucible). The heating rate was 1.1° C./min upto a temperature of 400° C., that was held for 4 hours.

Life Time Test (Method B)

1200 g of 2.0% F-doped Yttriumoxide were mixed with 360 g of AmmoniumZirconium Carbonate. The slurry showed a lifetime of 35.7 hours.

Example 21

The production of the F-doped Yttria was carried out as described inExample 20. The heating rate of the calcination was 1.1° C./min up to atemperature of 1100° C., that was maintained for 2 hours.

Life Time Test (Method B)

1200 g of 2.0% F-doped Yttriumoxide were mixed with 360 g of AmmoniumZirconium Carbonate. Due to the temperature treatment at 1100° C.relatively strong agglomerates were formed, in order to disperse theparticles homogenously and to break down the agglomerates, powder andbinder were mixed additionally to the agitator with an Ultra Turrax T25(2 min 13500 l/min). After 17.1 hours the viscosity has doubled.

Example 22

The production of the F-doped Yttria was carried out as described inExample 20. The heating rate of the calcination was 1.1° C./min up to atemperature of 900° C., that was maintained for 4 hours.

Life Time Test (Method B)

1200 g of 1.9% F-doped Yttriumoxide were mixed with 360 g of AmmoniumZirconium Carbonate.

Due to the temperature treatment at 900° C. relatively strongagglomerates were formed, in order to disperse the particleshomogenously and to break down the agglomerates, powder and binder weremixed additionally to the agitator with an Ultra Turrax T25 (30 sec13500 l/min and 10 sec 17500 l/min).

The shiny showed a lifetime of 16.3 hours.

Example 23

The production of the F-doped Yttria was carried out as described inExample 20. The heating rate of the calcination was 1.1° C./min up to atemperature of 800° C., that was maintained for 4 hours.

Life Time Test (Method B)

1200 g of 1.9% F-doped Yttriumoxide were mixed with 360 g of AmmoniumZirconium Carbonate. Due to the temperature treatment at 800° C.agglomerates were formed, in order to disperse the particleshomogenously and to break down the agglomerates, powder and binder weremixed additionally to the agitator with an Ultra Turrax T25 (30 sec13500 l/min)

The slurry showed a lifetime of 26.1 hours.

Example 24

The production of the F-doped Yttria was carried out as described inExample 20. The heating rate of the calcination was 1.1° C./min up to atemperature of 300° C., that was maintained for 4 hours.

Life Time Test (Method B)

1200 g of 2.1% F-doped Yttriumoxide were mixed with 360 g of AmmoniumZirconium Carbonate. The viscosity doubled after 26.7 hours.

Example 25

6.649 kg fused block material of Y/Al/Zr (95.88/0.12/4.0) were milledfor 30 minutes in a ball mill (ZOZ GmbH TYP COMB 03-A03; 20 kg 1.25″grinding-balls (Yttria stabilized Zirconium Oxide—other millingparameters as described in Example 1). After the addition of 0.351 kg(=5.0 wt %) Lanthanum fluoride the powder mixture was milled for another120 minutes. The milled product was sieved <63 μm and then calcined(Nabertherm C250; 1.5 kg per Al₂O₃(0.9)-mullite(0.1)-crucible). Theheating rate was 1.1° C./min up to a temperature of 550° C., that wasmaintained for 4 hours.

Life Time Test (Method B)

1200 g of 1.3% F-doped Y/Al/Zr were mixed with 360 g of AmmoniumZirconium Carbonate. The slurry showed a lifetime of 47.0 hours.

Example 26

6.570 kg fused block material of Y/Al/Zr (95.88/0.12/4.0) were milledfor 30 minutes in a ball mill (ZOZ GmbH TYP COMB 03-A03; 20 kg 1.25″grinding-balls (Yttria stabilized Zirconium Oxide—other millingparameters as described in Example 1). After the addition of 0.430 kg(=6.1 wt %). Ytterbium fluoride the powder mixture was milled foranother 120 minutes. The milled product was sieved <63 μm and thencalcined (Nabertherm C250; 1.5 kg per Al₂O₃(0.9)-mullite(0.1)-crucible).The heating rate was 1.1° C./min up to a temperature of 550° C., thatwas maintained for 4 hours.

Life Time Test (Method B)

1200 g of 1.6% F-doped Y/Al/Zr were mixed with 360 g of AmmoniumZirconium Carbonate. The slurry showed a lifetime of 44.7 hours.

Example 27

6.617 kg fused block material of Y/Al/Zr (50/25/25) were milled for 30minutes in a ball mill (ZOZ GmbH TYP COMB 03-A03; milling parameters asdescribed in Example 1). After the addition of 0.383 kg (=5.5 wt %)Zirconiumoxyfluoride Zr₇O_(8.79)F_(9.71) the powder mixture was milledfor another 120 minutes. The milled product was sieved <63 μm and thencalcined (Nabertherm C250; 1.5 kg per Al₂O₃(0.9)-mullite(0.1)-crucible).The heating rate was 1.1° C./min up to a temperature of 400° C., thatwas maintained for 4 hours.

Life Time Test (Method B)

1200 g of 1.7% F-doped Y/Al/Zr were mixed with 380 g of AmmoniumZirconium Carbonate. After a certain time the volume of the slurry wastoo small to realise Zahncup Nr. 5 measurements. Therefore Rheometermeasurements (measuring gap=1 mm) were made. First every weekday,afterwards approximately every week one respectively two measurementswere realised. No significant increase of the viscosity of theformulated slurry could be observed for 150 days. Afterwards theexperiment was stopped.

The summary of the results is presented in Table 1.

TABLE 1 Summary of the results heating rate calcination dwell Rawmaterial Dopant Fluorine [° C./ temperature time Test binder RatioSlurry Example flour flour [wt %] min] [° C.] [h] method systembinder:flour(:H₂O) lifetime [h] Comparative Y/Al/Zr-Oxide — — — — —Method A Ammonium 1:5.58:0.49 0.9 Example 1 (95.88/0.12/4) ZirconiumCarbonate Comparative Y/Al/Zr-Oxide — — — — — Method A Zirconium1:5.58:0.49 0.7 Example 2 (95.88/0.12/4) Acetate  1 Y/Al/Zr-Oxide YF₃0.8 5   550 6 h Method A Zirconium 1:5.58:0.49 41 (95.88/0.12/4) 50 minAcetate  2 Y/Al/Zr-Oxide YF₃ 0.8 5   550 6 h Method A Ammonium1:5.58:0.49 56 (95.88/0.12/4) 50 min Zirconium Carbonate  3Y/Al/Zr-Oxide Zirkonyl- 1.0 — 550 3 Method A Ammonium 1:5.58:0.49 124(95.88/0.12/4) fluoride Zirconium Carbonate  4 Y/Al/Zr-Oxide YF₃ 0.9 5  540 8 Method A Zirconium 1:4 66 (95.88/0.12/4) Acetate  5 Y/Al/Zr-OxideZrF₄ 0.8 — 550 3 Method A Ammonium 1:5.58:0.49 380 (95.88/0.12/4)Zirconium Carbonate  6 Y₂O₃ Zr₇O_(8.79)F_(9.71) 1.9 — 400 4 Method AAmmonium 1:3.3 >335 Zirconium Carbonate  7 Y2O3 LiF 1.7 — 400 4 Method AAmmonium 1:3.3 10 Zirconium Carbonate Comparative Y/Al/Zr-Oxide — — — —— Method B Ammonium 1:3.3 <3 Example 3 (95.88/0.12/4) ZirconiumCarbonate Comparative Y/Al/Zr-Oxide — — — — — Method B Zirconium 1:4 <35min Example 4 (95.88/0.12/4) Acetate Comparative Y₂O₃ — — — — — Method BAmmonium 1:3.3 <3 Example 5 Zirconium Carbonate  8 Y/Al/Zr-Oxide YF₃ 1.01.1 550 8 Method B Zirconium 1:4 72 (95.88/0.12/4) Acetate  9Y/Al/Zr-Oxide Zr₇O_(8.79)F_(9.71) 1.1 1.1 450 4 Method B Zirconium 1:4After 171.5 (95.88/0.12/4) Acetate hours start- η increased by 85% 10Y/Al/Zr-Oxide Zr₇O_(8.79)F_(9.71) 2.2 1.1 650 13  Method B Ammonium1:3.3 28.7 (95.88/0.12/4) Zirconium Carbonate 11 Y/Al/Zr-OxideZr₇O_(8.79)F_(9.71) 2.4 1.1 450 7 Method B Ammonium 1:3.3 70.3(95.88/0.12/4) Zirconium Carbonate 12 Y/Al/Zr-Oxide Zr₇O_(8.79)F_(9.71)1.7 1.1 400 4 Method B Ammonium 1:3.6 44.9 (95.88/0.12/4) ZirconiumCarbonate 13 Y/Al/Zr-Oxide Zr₇O_(8.79)F_(9.71) 0.1 1.1 400 4 Method BAmmonium 1:3.3 21.6 (95.88/0.12/4) Zirconium Carbonate 14 Y/Al/Zr-OxideZr₇O_(8.79)F_(9.71) 6.9 1.1 400 4 Method B Ammonium 1:2.7 >110 days(95.88/0.12/4) Zirconium Carbonate 15 Y₂O₃ Zr₇O_(8.79)F_(9.71) 1.9 1.1400 4 Method B Ammonium 1:3.3 74.1 Zirconium Carbonate 16 Y₂O₃Zr₇O_(8.79)F_(9.71) 1.9 1.1 1100 4 Method B Ammonium 1:3.3 26.5Zirconium Carbonate 17 Y₂O₃ Zr₇O_(8.79)F_(9.71) 2.0 1.1 900 4 Method BAmmonium 1:3.3 26.9 Zirconium Carbonate 18 Y₂O₃ Zr₇O_(8.79)F_(9.71) 1.91.1 800 4 Method B Ammonium 1:3.3 33.4 Zirconium Carbonate 19 Y₂O₃Zr₇O_(8.79)F_(9.71) 2.0 1.1 300 4 Method B Ammonium 1:3.3 50.3 ZirconiumCarbonate 20 Y₂O₃ YF₃ 2.0 1.1 400 4 Method B Ammonium 1:3.3 35.7Zirconium Carbonate 21 Y₂O₃ YF₃ 2.0 1.1 1100 2 Method B Ammonium 1:3.317.1 Zirconium Carbonate 22 Y₂O₃ YF₃ 1.9 1.1 900 4 Method B Ammonium1:3.3 16.3 Zirconium Carbonate 23 Y₂O₃ YF₃ 1.9 1.1 800 4 Method BAmmonium 1:3.3 26.1 Zirconium Carbonate 24 Y₂O₃ YF₃ 2.1 1.1 300 4 MethodB Ammonium 1:3.3 26.7 Zirconium Carbonate 25 Y/Al/Zr-Oxide LaF₃ 1.3 1.1550 4 Method B Ammonium 1:3.3 47.0 (95.88/0.12/4) Zirconium Carbonate 26Y/Al/Zr-Oxide YbF₃ 1.6 1.1 550 4 Method B Ammonium 1:3.3 44.7(95.88/0.12/4) Zirconium Carbonate 27 Y/Al/Zr-Oxide Zr₇O_(8.79)F_(9.71)1.7 1.1 400 4 Method B Ammonium 1:3.2 >150 days (50/25/25) ZirconiumCarbonate

1. Yttria-based refractory composition obtainable by a methodcomprising: (a) mechanically mixing particles of an yttria-based ceramicmaterial and a fluorine-containing dopant other than an an alkali metalfluoride, wherein said yttria-based ceramic material comprises Y/Al/Zroxide or Y/Zr oxide, from 50 wt.% up to less than 100 wt.% Y₂O₃, 0-50wt.% Al₂O₃, and more than 0% and up to 50 wt.% ZrO₂, and (b) heating theresulting mixture to a temperature within a range of 300-800° C. toeffect fluorine-doping of said yttria-based ceramic material and yieldan yttria-based ceramic material doped with fluorine.
 2. Yttria-basedrefractory composition according to claim 1, wherein saidfluorine-containing dopant is selected from the group consisting of YF₃,AlF₃, ZrF₄, lanthanide fluorides, and zirconium oxyfluoride. 3.Yttria-based refractory composition according claim 2, wherein theyttria-based refractory composition comprises 0.1-7.5 wt.% fluorine. 4.Yttria-based refractory composition obtainable by a method comprising:(a) mechanically mixing particles of an yttria-based ceramic materialand a fluorine-containing dopant other than an alkali metal fluoride,wherein said yttria-based ceramic material comprises Y/Al/Zr oxide orY/Zr oxide, from 50 wt.% up to less than 100 wt.% Y₂O₃, 0-50 wt.% Al₂O₃,and more than 0% and up to 50 wt.% ZrO₂; and (b) heating the resultingmixture to a temperature within a range of 300-800° C. to effectfluorine-doping of said yttria-based ceramic material and yield anyttria-based ceramic material doped with fluorine, wherein theyttria-based refractory composition comprises 0.1-7.5 wt.% fluorine. 5.Yttria-based refractory composition obtainable by a method comprising:(a) mechanically mixing particles of an yttria-based ceramic materialand a fluorine-containing dopant, wherein said yttria-based ceramicmaterial comprises Y/Al/Zr oxide or Y/Zr oxide and saidfluorine-containing dopant is selected from the group consisting of YF₃,AlF₃, ZrF₄, lanthanide fluorides, and zirconium oxyfluoride; and (b)heating the resulting mixture to a temperature within a range of300-800° C. to effect fluorine-doping of said yttria-based ceramicmaterial and yield an yttria-based ceramic material doped with fluorine,wherein the yttria-based refractory composition comprises 0.1-7.5 wt.%fluorine.
 6. Yttria-based refractory composition according to claim 1,wherein said yttria-based ceramic material comprises Y/Al/Zr oxide. 7.Yttria-based refractory composition according to claim 1, wherein saidyttria-based ceramic material comprises Y/Zr oxide.
 8. Yttria-basedrefractory composition according to claim 4, wherein said yttria-basedceramic material comprises Y/Al/Zr oxide.
 9. Yttria-based refractorycomposition according to claim 4, wherein said yttria-based ceramicmaterial comprises Y/Zr oxide.
 10. Yttria-based refractory compositionaccording to claim 5, wherein said yttria-based ceramic materialcomprises Y/Al/Zr oxide.
 11. Yttria-based refractory compositionaccording to claim 5, wherein said yttria-based ceramic materialcomprises Y/Zr oxide.